Easier to show remote tracking relationship in Log List

These changes make it eaiser show remote tracking relationship in Log List.

1: If a local branch has remote tracking branch, indicate that, currently a round rectangle. 
![LogDialog-HasTracking-g5ac5e70](https://f.cloud.github.com/assets/2804967/37215/cfb5ff66-5409-11e2-8ca6-fe6eff1b6d72.png)


2: Put remote tracking branch next to the corresponding local branch.
![LogDialog-HasTracking-gcd11a7a](https://f.cloud.github.com/assets/2804967/37216/dc094e76-5409-11e2-8d7f-628986279408.png)


3: Simplify remote tracking branch name, can shorten the label width.
![LogDialog-HasTracking-g62db8ca](https://f.cloud.github.com/assets/2804967/37217/e171a3a4-5409-11e2-9428-62a8d9fa9ed6.png)